L. J. E. Hofer

Classical Thermodynamics and Reaction Rates Close to Equilibrium

For reversible reactions close to equilibrium the net reaction rate (rf—rb) is shown to be proportional to ΔX, where X is any one of the thermodynamic functions, e.g., the Gibbs free energy, F, governing equilibrium under the conditions of the reaction, e.g., (rf—rb)=rf·—ΔF /RT. The derived relationships are independent of the manner in which small displacements from equilibrium may be brought about. Equations are derived by which the magnitude of the forward (or backward) reaction rate at equilibrium may be determined with the aid of observations of the net reaction rate close to equilibrium. Since the magnitude of the former is a function of the kinetics of the reaction, measurements of the net reaction rate near equilibrium over a range of conditions may be used within specified limits to determine the kinetics of reversible reactions.

Some Thermal Reactions of the Higher Iron Carbides

One of the undesirable side reactions of the Fischer‐Tropsch synthesis is deposition of carbon. To ascertain whether thermal reactions of iron carbides might cause this deposition and to learn more about the nature of iron carbides, the transition from hexagonal close‐packed (h.c.p.) iron carbide to Hagg iron carbide and the reaction of higher iron carbide with metallic iron to form cementite have been studied in a copper‐ and alkali‐promoted iron catalyst by means of a magnetic balance.The transition from h.c.p. to Hagg iron carbide is heterogeneous, with no apparent change of the compositions of both carbides, nor any detectable solubility of one carbide in the other. The data confirm the narrow range of composition of Hagg carbide and the fact that it contains somewhat more iron than corresponds to the formula Fe2C.The synthesis of cementite from metallic iron and higher iron carbide proceeds via Hagg carbide and only above about 320°C. It does not go to completion up to 440°C; above that temperature, ...